Prevention of mould growth is an important topic to the food, feed and agricultural industry, as fungal spoilage can lead to considerable economic losses. Some products can be considered as good substrates for fungal growth. Cheeses and sausages are examples of such products. Apart from the negative appearance of fungal growth on food, feed and agricultural products, fungal spoilage can also become a health risk. It is known that some mould species that contaminate food, feed and agricultural products can produce mycotoxins which can penetrate into the products (see Frisvad and Thane (1995)). Consequently, superficial removal of moulds gives no guarantee of safety to the consumer.
For more than 30 years, natamycin has been used to prevent growth of moulds and yeasts on a variety of products including food products such as cheeses and sausages. Natamycin is a natural polyene macrolide antifungal compound produced by fermentation of bacteria such as Streptomyces natalensis. Natamycin has an extremely effective and selective mode of action against a very broad spectrum of common food spoilage yeasts and moulds with most strains being inhibited by concentrations as low as 1-15 ppm. Despite its long-term use, the development of resistant strains against natamycin has not been reported to date unlike the chemical organic acid sorbate and propionate preservatives for which a number of resistant yeasts and moulds have been detected and reported.
There exist several ways by which food, feed and agricultural products can be treated with natamycin. For example, natamycin can be added to an emulsion of a polymer in water, mostly polyvinyl acetate, which can be applied as a coating on a product such as for example cheese (see Daamen and Berg (1985)). Products, e.g. cheeses or sausages, can also be treated by immersion or spraying with a suspension of natamycin in water (see Morris and Castberg (1980)). Usually polymer emulsions for coating purposes contain 0.01 to 0.05% (w/v) of natamycin, while aqueous suspensions for immersion treatments contain 0.1 to 0.2% (w/v) of natamycin and aqueous suspensions for spraying contain 0.1 to 1.5% (w/v) of natamycin, respectively.
Natamycin is on the market under the brand name of DELVOCID®, a powder composition containing natamycin and a thickening agent, e.g. xanthan gum. Currently, aqueous natamycin compositions are prepared by weighing the powder and mixing it with water. Salt is added to the aqueous natamycin compositions to improve the drying properties of the composition on the product and to increase microbiological stability of the compositions. This results in a final antifungal composition having a pH of around 6 that can effectively be used in the prevention of fungal spoilage (see EP 0 867 124). However, the use of the composition gives rise to significant problems with respect to corrosion of process equipment such as machines used in food processing plants.